linux-kernel - [PATCH 3.2 043/185] IB/ipath: Convert ipath_user_sdma_pin_pages() to use get_user_pages

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Date:	Sun, 29 Dec 2013 03:08:43 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org,
	"Mike Marciniszyn" <mike.marciniszyn@...el.com>,
	"Roland Dreier" <roland@...estorage.com>, "Jan Kara" <jack@...e.cz>
Subject: [PATCH 3.2 043/185] IB/ipath: Convert ipath_user_sdma_pin_pages()
 to use get_user_pages_fast()

3.2.54-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Jan Kara <jack@...e.cz>

commit 4adcf7fb6783e354aab38824d803fa8c4f8e8a27 upstream.

ipath_user_sdma_queue_pkts() gets called with mmap_sem held for
writing.  Except for get_user_pages() deep down in
ipath_user_sdma_pin_pages() we don't seem to need mmap_sem at all.

Even more interestingly the function ipath_user_sdma_queue_pkts() (and
also ipath_user_sdma_coalesce() called somewhat later) call
copy_from_user() which can hit a page fault and we deadlock on trying
to get mmap_sem when handling that fault.  So just make
ipath_user_sdma_pin_pages() use get_user_pages_fast() and leave
mmap_sem locking for mm.

This deadlock has actually been observed in the wild when the node
is under memory pressure.

Signed-off-by: Jan Kara <jack@...e.cz>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@...el.com>

[ Merged in fix for call to get_user_pages_fast from Tetsuo Handa
  <penguin-kernel@...ove.SAKURA.ne.jp>.  - Roland ]

Signed-off-by: Roland Dreier <roland@...estorage.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/infiniband/hw/ipath/ipath_user_sdma.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

--- a/drivers/infiniband/hw/ipath/ipath_user_sdma.c
+++ b/drivers/infiniband/hw/ipath/ipath_user_sdma.c
@@ -280,9 +280,7 @@ static int ipath_user_sdma_pin_pages(con
 	int j;
 	int ret;

-	ret = get_user_pages(current, current->mm, addr,
-			     npages, 0, 1, pages, NULL);
-
+	ret = get_user_pages_fast(addr, npages, 0, pages);
 	if (ret != npages) {
 		int i;

@@ -811,10 +809,7 @@ int ipath_user_sdma_writev(struct ipath_
 	while (dim) {
 		const int mxp = 8;

-		down_write(&current->mm->mmap_sem);
 		ret = ipath_user_sdma_queue_pkts(dd, pq, &list, iov, dim, mxp);
-		up_write(&current->mm->mmap_sem);
-
 		if (ret <= 0)
 			goto done_unlock;
 		else {

--
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